Vulcanization of rubber



'anhydride addition product or adduct.

Patented July 7, 1942 VULCANIZATION OF RUBBER Theodore F. Bradley, Stamford, Comn, assignor to American Cyanamid Company, New York, N. Y., a corporation of Maine No Drawing. Application January 25, 1940,

Serial No. 315,534

8 Claims.

This invention relates to vulcanization of rubber and more particularly to the control of the activity of accelerators employed in the vulcanization.

Sulfur-bearing materials such as mercaptobenzothiazole, benzothiazyl disulfide and the like have been used as accelerators of the vulcanization of rubber. Other accelerators used may be classified as organic sulfur compounds which are acidic or which hydrolyze. to produce mercaptans or thio acids. These accelerators, in general, become more active in the presence of certain basic substances including the diaryl guanidines, such, for example, as diphenyl guanidine, di-ortho-tolyl guanidine, phenyl-orthotolyl guanidine and the like. However, these latter substances are apt to cause set-up or scorching in the rubber during the preliminary processing such as milling, calendering, extruding, etc., prior to the desired vulcanizing of the rubber, and they may even cause premature vulcanization of the rubber during storage.

It is an object of the invention, therefore, to provide for the retardation of the activity of the diaryl guanidines when used as activators for the sulfur-bearing accelerators.

This and other objects are attained by incorporating in the rubber mix a diterpene-maleic The adduct which is a dibasic acid anhydride or a mixture of isomeric dibasic acid anhydrides may be hydrolysed in known manner to obtain the dibasic acid or acids which may be employed in place of the adduct. In the specification and claims it is intended that the term addition product or adduct include also the free dibasic acid or acids.

The diterpene-maleic anhydride adducts may be prepared by heating a diterpene of the formula C2oH32 with maleic anhydride or its equivalent of maleic acid and purifying the resinous product by distillation to remove unreaoted materials and traces of low molecular weight impurities. Water-soluble materials in the resinous residue such as unreacted maleic anhydride may be extracted with water. Such a process of preparing the addition products or adducts is more particularly described in my application, Serial Number 51,498 filed November 25, 1935, now Patent No. 2,208,321.

The non-volatile resinous residue obtainable in accordance with the above process consists essentially of dibasic acid anhydrides of unsaturated nature. Chemically, these anhydrides are probably a mixture or isomers having the formula C24H3403 and a molecular weight of 370.

The invention will be illustrated by the following examples to which, however, the invention is not to be limited. Unless otherwise specified, proportions are given .by weight.

Example 1 Samples were compounded to contain diphenyl guanidine in each case. Two of the samples contained in adidtion dissimilar quantities of a diterpene-maleic anhydride adduct. The ingredients in the following proportions were incorporated in the rubber by milling the mix on rolls in the customary way.

Compounds A B O Smoked sheets 100 100 Zinc oxide 6 6 6 Sulphur l 3 3 .75 .75 .75 Diphenyl guanidine .445 .445 .445 Diterpene-maleic anhydride adduct .80 40 Compounds A B O No heat incl1es.. .073 072 .075 After two hours in water at 85 0. .do .230 .079 131 Change percent +215 +9. 7 +74. 8

It can readily be seen from these tests that the adduct gives a slower rate of set-up than the diphenyl guanidine alone.

The samples were then tested at full cure:

Compounds 25-minute cure at C.

Stress lbs/sq. in. at 500% elongation l, 580 l, 315 l, 465 Tensile lbs/sq. in. 4, 245 4,100 4,1 l0 Percent elongation 650 670 Gal) These tensile tests show that the diterpenemaleic anhydride adduct gives approximately the same physical properties as those obtained with the free or unretarded diphenyl guanidine.

In the following example diterpene-maleic anhydride adduct was tested as a retarder for diortho-tolyl guanidine in accordance with the procedure of Example 1.

Example 2 The samples were made up in the usual manner. As shown below one of the samples contained a quantity of adduct in addition to the diortho-tolyl guanidine.

Compounds Smoked sheets 100 100 Zinc oxide 6 Sulfur 3 Benzothiazyl disulfide .75 Di-ortho-tolyl guanidin .31 Diterpene-malcic anhydride add .240

These samples were then given a set-up test in the Williams plastometer at 100 C. using a three minute 2/ value in inches.

Compounds No heat inches... .066 .068 After two hours in water at 85 0.. do. .132 .092 Change perccnt. +100 +35. 3

The above results show that the adduct gave a slower rate of set-up than the di-ortho-tolyl guanidine alone.

These physical tests show that di-ortho-tolyl guanidine retarded with diterpene-maleic anhydride adduct gives practically the same physical properties as those obtained with the free di-ortho-tolyl guanidine.

The above examples demonstrate the utility of the adducts in reducing the activity at processing temperatures of the diaryl guanidine activators. It is to be noted that the delaying action of the adducts on the diaryl guanidines is efiective regardless of the presence or absence of a sulfur bearing accelerator. Accordingly, the adducts may be used to delay the action of the diaryl guanidines not only when the latter are employed as activators but also when they are present in the rubber as the sole accelerator. Wellknown diaryl guanidine accelerators are diphenyl guanidine and di-ortho-tolyl guanidine.

The value of the adducts in the vulcanization of rubber is not, however, limited to their use with the diaryl guanidines, but they may be employed to retard the sulfur-bearing accelerators and especially the accelerators of this group which have the greater activity at the lower or processing temperatures.

The following example illustrates the capacity of the adducts to retard the sulfur-bearing accelerators. In this example the more active accelerator, mercaptobenzothiazole, was employed.

Example 3 A diterpene-maleic anhydride adduct in diferent quantities was incorporated in samples along with equal amounts of the accelerator. In addition one of the samples was made up to contain mercaptobenzothiazole alone. The several ingredients were compounded as follows.

Compounds F G H Smoked sheets 100 100 Zinc oxide 6 6 6 Sulfur 3 3 3 Mercaptobenzoth 201 1 1 l Stearic acid l 1 1 Diterpene-maleic anhydride addu 25 When tested in a Williams plastometer at 100 C. using a three minute y value in inches the following results were obtained.

Compounds F G H No heat "inches" .080 .078 .085 After two hours in water at 85 C do. .103 122 Change percent +75 +32 +43. 5

From the above it can be readily seen that the mercaptobenzothiazole was in each case retarded by the presence of the adduct.

The samples were then tested at full cure:

Compounds 30-minute cure at 141 C.

F G H I Stress lbs/sq. in. at 500% elongation 520 490 500 Tensile lbs/sq. in 3,305 3, 570 3, 745 Percent elongation 815 825 830 The above tensile tests indicate that while the adducts retard mercaptobenzothiazole at 85 0.,

or at processing temperatures, they have little or no effect on the accelerator at the vulcanizing temperature.

It is an additional advantage of the present invention that the resinous adducts will more easily disperse in rubber than the activator retarders which are crystalline and have high melting points, such, for example, as benzoic acid, salicylic acid, etc.

' Theproportions given in the foregoing examples are not intended to be limiting of the invention since they may be varied, as will be understood by those skilled in the art, in accordance with the particular diaryl guanidine or' 6. A vulcanizable rubber mix having incorporated therein a diterpene-maleic anhydride addition product, a diaryl guanidine and an organic sulfur-bearing vulcanization accelerator.

7. A vulcanizable rubber mix in accordance with claim 6, in which the diaryl guanidine is diphenyl guanidine.

8. A vulcanizable rubber mix in accordance with claim 6, in which the diaryl guanidine is addition product and an organic sulfur-bearing 10 di-ortho-tolyl guanidine.

vulcanization accelerator.

THEODORE F. BRADLEY. 

